1. Field of the Invention
The present invention relates to a method of and an apparatus for inspecting the line width on a printed board, and more particularly, it relates to an improvement for detecting respective lines having different width.
2. Description of the Background Art
As electronic parts have been reduced in size and in weight as well as have been improved in performance, a wiring patterns on printed board circuits have been also highly refined and integrated. Accordingly, required are narrow wiring lines in wiring patterns and small diameters of through holes in printed boards.
As to such narrowed lines, inspection and management of widths, disconnection, or short-circuiting etc. thereof are regarded as more important than before.
In such inspection and management of line width of a wiring pattern, an allowable range of width is previously determined. Then, the line width is compared with the allowable range. When the line width is in the allowable range, it is concluded that the line is not defective. On the other hand, when the line width is out of the allowable range, it is concluded that the line is defective.
In order to obtain the line width, the printed board is photoelectrically scanned to obtain a wiring pattern image of the printed board. The pattern image is binarized to obtain image data, which in turn is subjected to various processings including the above-indicated comparative procedure for determining whether the pattern is defective or not. One of the methods effective for processing the binarized pattern image is a processing with a pixel operator, which is disclosed in Japanese Patent Laying-Open Gazette No. 59-74627 (1984), for example.
However, line width is not constant and varies in the range from about 80 to 400 .mu.m with the types of printed boards to be inspected, for example. Further, lines of different width may be provided on a single printed board. Thus, the line width should be detected depending upon the type of each board or each line.
For example, it is supposed that a narrow line L.sub.1 (FIG. 19) and a wide line L.sub.2 (FIG. 20) are formed on the same printed board. In order to accurately measure the width of the narrow line L.sub.1, an pixel operator should be applied to a pixel matrix T having a high resolution or fineness. On the other hand, the width of the wide line L.sub.2 cannot be measured with a small-scale operator, and therefore, the two dimensional size or the number of pixels in the matrix T should be large under the condition that the resolution in the matrix T is maintained. Further, when a pixel operator is applied to the large-scale matrix space, a number of bits are required to represent the result of the application of the pixel operator and subsequent logical operations on the resultant data becomes complicated.
Japanese Patent Laying-Open Gazette No. 63-78009 discloses a method to solve this problem. In this method, a plurality of pixel operators having different resolutions are defined. A pixel operator having a high resolution is first applied to the line image, and when the high-resolution operator is overflown, a coarse pixel operator is selected in place of the high-resolution operator to thereby obtain an optimum resolution for each line or each printed board. However, this method requires a plurality of pixel operators adapted for the respective resolutions depending upon the line width, and a processing part for switching the operators is required.